If you like a creature so much that you want an entire army of them, Rionya, Fire Dancer is the commander for you. Her ability allows us to copy a creature once, plus an additional time for each instant and sorcery we've cast this turn. Since they gain haste and are exiled at the end of the turn, we will be making use of powerful ETB effects as well as "whenever this creature attacks" effects to make the most of our short-lived instant army. We'll also want to do whatever we can to ensure that we can continue casting many, many spells so that we can actually make use of this powerful ability.
While you may indeed have a favorite creature card, we'll want to run plenty of copy-friendly creatures in case our inconsiderate opponents decide to remove some of them. I especially like Zealous Conscripts, as it allows us to steal our opponents best creature, copy it many times, and then steal the rest of their creatures, leaving them utterly defenseless against their board that they worked so hard to build up. Lower end creatures can be copied for some value in order to get us to more powerful bomb creatures. For example, Humble defector will allow us to draw plenty of cards, giving away only tapped soon-to-be-exiled copies, and Wily Goblin can give us a stack of treasures in order to cast more of a powerhouse next turn. Utvara Hellkite and Terror of the Peaks will be, well, an absolute terror for your enemies as you turn your temporary army into a sizable permanent advantage.
The next piece of the puzzle will be to pack the deck full of spells to increase the number of copies that we can make per turn. The best way to generate more copies will be to cast cheap spells that replace themselves, however any spell with powerful effects are fine to include in the deck as well. We will also make use of any rituals we can find, increasing our spell count by one and giving us more mana to cast additional spells. Cards like Commune with Lava and Finale of of Promise are perfect ways to play lots of cheap spells in one turn, ideally playing multiple cantrips for the cost of one card and ramping up Rionya's copy ability.
Now that we have both creatures to copy and spells to build up Rionya's ability, there's even more we can do. For each extra combat phase, we will generate a new batch a creature copies. It will take a lot of mana to gain additional combat phases after playing a decent number of instants and sorceries, but it can pay off handsomely and push us to victory. Aggravated Assault is especially potent in our deck, since it can create more combat phases at any time. Pair it with Wily Goblin or Dockside Extortionist for an endless loop of mana and creatures!
There's a few useful artifacts that we can include to spice things up. Of course, we'll want mana rocks to get Rionya out faster. But there's also Strionic Resonator, which can double the amount of tokens that we put out during combat for only 2 mana. Also, Idol of Oblivion will be an easy way to draw a card each turn, as long as we have a single creature on the board to copy.
As a mono-red deck, you can definitely get away with running full basic mountains. However, here are a few options to improve your land base.
That's all we've got for now! We're currently working on a budget version of this deck to include in our Custom Decks collection for sale, so check back for that soon!
